Some of the neurons in the nucleus intercollicularis and auditory cortex of the echolocating bat Eptesicus fuscus respond selectively to sonar echoes occurring with specific echo delays or pulse-echo intervals. They do not respond for a wide range of other types of sounds or for sonar echoes at longer or shorter pulse-echo intervals; they may, therefore, be specialized for detection and ranging of sonar targets.

Echolocating bats (Eptesicus fuscus) perceive either monaurally or binaurally the range of sonar targets with an acuity of about 1 cm, or a time delay acuity of about 60 μsec. Single-unit recordings from cortical and midbrain auditory neurons in unanesthetized bats indicate response properties to stimuli consisting of pairs of simulated echolocation signals (three-harmonic descending FM sweeps with energy from 23 to 100 kHz) with naturally occurring transmission-echo time delays and intensity differences. While many neurons respond to both transmissions and echoes given sufficient intensities and long echo delays, some neurons respond exclusively to the pair when the time delay is within a narrow range. Their temporal response selectivity increases with decreasing overall absolute transmission-echo intensity but is independent of intensity differences between transmissions and echoes. These results demonstrate “tuning” of central auditory neurons to specific echo delays, providing the neural basis for target range perception in bats and possibly perception of temporal structure of sounds in other animals. [Work supported by NSF and NIH.]